| Alice has $a$ coins. She can open a bank deposit called "Profitable", but the minimum amount required to open this deposit is $b$ coins. | |
| There is also a deposit called "Unprofitable", which can be opened with any amount of coins. Alice noticed that if she opens the "Unprofitable" deposit with $x$ coins, the minimum amount required to open the "Profitable" deposit decreases by $2x$ coins. However, these coins cannot later be deposited into the "Profitable" deposit. | |
| Help Alice determine the maximum number of coins she can deposit into the "Profitable" deposit if she first deposits some amount of coins (possibly $0$) into the "Unprofitable" deposit. If Alice can never open the "Profitable" deposit, output $0$. | |
| Each test consists of multiple test cases. The first line contains a single integer $t$ ($1 \le t \le 10^4$) — the number of test cases. The description of the test cases follows. | |
| A single line of each test case contains two integers $a$ and $b$ ($1 \le a, b \le 10^9$) — the number of coins Alice has and the initial minimum amount required to open the "Profitable" deposit. | |
| For each test case, output a single integer — the maximum number of coins that Alice can deposit into the "Profitable" deposit. If Alice can never open the "Profitable" deposit, output $0$. | |
| In the first test case, $a \ge b$, so Alice can immediately open the "Profitable" deposit with all $10$ coins. | |
| In the second test case, Alice can open the "Unprofitable" deposit with $2$ coins. Then she will have $5$ coins left, but the minimum amount required to open the "Profitable" deposit will decrease by $4$ coins, making it equal to $5$ coins. Thus, Alice will be able to open the "Profitable" deposit with $5$ coins. | |
| In the third test case, Alice will not be able to open the "Profitable" deposit. |